How to Resolve HTTP 404 Errors in Azure Function App After Migrating from .NET 6 to .NET 8?

Question:

I recently migrated my Azure Function App from .NET 6 to .NET 8, and initially, everything was working smoothly. However, after some time, I started encountering multiple HTTP 404 errors, which impacted over 1,000 requests within a 24-hour period.
ErrorMessage

Details of My Problem:

• Migration Context: The migration from .NET 6 to .NET 8 was completed, and all functions were executing correctly right after the transition.

• Issue Occurrence: After some time, I began receiving 404 Not Found errors for various endpoints that were functioning properly prior to migration.

• Impact: These errors caused downtime and a poor user experience, affecting over 1,000 requests in 24 hours.

• Logs Analysis: I reviewed both API Management and function logs but couldn’t identify the root cause.

What I Tried:

• Verified the migration process and ensured application settings were correct.

• Reviewed API Management and function logs for discrepancies.

• Checked routing configurations to make sure they aligned with .NET 8’s setup.

Problem:

I expected the migration to .NET 8 to improve the performance and reliability of my Azure Function App. Instead, I encountered a spike in HTTP 404 errors that were not present in .NET 6.

Here’s a simplified code snippet of one of my Azure Functions:

[Function("MyFunction")]
public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = "myendpoint/{id}")] HttpRequest req, 
    ILogger log, 
    string id)
{
    log.LogInformation("Processing request for ID: " + id);

    if (string.IsNullOrEmpty(id))
    {
        return new BadRequestObjectResult("ID is required.");
    }

    // Simulate processing the request
    var result = await SomeService.ProcessAsync(id);
    
    if (result == null)
    {
        return new NotFoundResult(); // This is where the 404 error occurs
    }

    return new OkObjectResult(result);
}

host.json:

{
  "version": "2.0",
  "functionTimeout": "00:10:00"
}

local.settings.json:

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated"
  }
}

Logs:

Here’s an example of the 404 error logged:

HttpRequest failed with status code 404 for /myendpoint/1234

Expected Behavior:

When calling the function with a valid id, I expect it to return a 200 OK response with the processed result. However, after migration, many valid requests are resulting in 404 errors.